Biometric authentication technologies for performing authentication based on features of a body part, such as a fingerprint, veins, a facial image, and an iris, have been put into practical use. Biometric authentication requires a registration stage at which biometric features of a user are obtained in advance by a sensor and stored in a storage. Thereafter, at a verification stage, biometric features obtained by a sensor are verified in comparison with the biometric features stored, at the registration stage, in the storage.
What is important for appropriately achieving the biometric authentication is whether or not the same biometric features as those obtained at the registration stage may be obtained at the verification stage. In biometric authentication based on palm veins, for example, high-accuracy authentication may not be performed by capturing and storing feature data of palm veins of an upper right part of one's palm at the time of registration and capturing feature data of palm veins of a lower left part of the palm at the time of verification.
In order to conduct biometric authentication with high accuracy, it is important to obtain biometric features of the same area both at the time of verification and of registration. This issue has been a common challenge for almost all biometric authentication technologies, and some schemes have been proposed.
For example, Japanese Laid-open Patent Publication No. 2001-273498 discusses an apparatus which displays, on a screen, a guide pattern in the shape of a body-part contour to indicate an ideal capturing position and superimposes a body-part image captured with a sensor when obtaining biometric features at the time of verification. Japanese Laid-open Patent Publication No. 2007-58643 discusses a finger-vein authentication apparatus which has a fingertip guide movable back and forth with which a tip of a finger makes contact. The position of the fingertip guide at the time of registration is recorded to be reproduced at the time of verification. In addition, Japanese Laid-open Patent Publication No. 2007-122368 discusses a system which displays, at the time of verification, a contour image captured at the time of registration on a screen. The system also displays an image captured at the time of verification for comparison with the image obtained at the time of registration.
These proposed biometric authentication schemes suppose that the sensor used at the registration stage and the sensor used at the verification stage have the same shape. In some cases, however, the shape of the sensor used at the registration stage may be different from the shape of the sensor used at the verification stage. Examples of such cases include a case in which a verification sensor, i.e. a sensor used at the time of verification, has a detection area, i.e. an area where biometric-features are obtained, smaller than that of a registration sensor, i.e. a sensor used at the time of registration. Another example is a case in which cameras are used as sensors and the camera used at the time of verification has smaller eyeshot than the camera used at the time of registration. When the area of a body part that may be obtained at the time of verification is smaller that the area of a body part obtained at the time of registration, an authentication apparatus may not figure out with which area of the body part obtained at the time of registration it should align the body part obtained at the time of verification. Thus, it takes time for the verification. In addition, erroneous alignment may cause authentication error, such as coincidence with a different person's data.
In addition, when the distribution of biometric features is uneven, the amount of information of the obtained biometric features varies depending on the position where the biometric features are obtained by a sensor at the time of registration. Naturally, for a part where the amount of information of obtained biometric features is small, the amount of information that may be used for authentication is smaller compared to a part where the amount of information is large. As a result, the authentication accuracy may decrease. When the part from which biometric features are obtained is not a suitable part for biometric authentication, high-accuracy biometric authentication may not be performed even when biometric features are obtained from the same part both at the time of registration and of verification.